The officer has been put on administrative leave pending an investigation.

Police handling of the affair has been widely criticised for a heavy handed approach.

Violence flared again on Saturday night when police cleared a hot spot outside a barbecue restaurant in Ferguson, after they identified armed men among the crowd. Officers used tear gas and wooden rounds to disperse protesters.

While those crowds have mostly comprised African-Americans, the protest in nearby downtown St Louis on Sunday was all white, except for a single black figure.

Many expressed exasperation with media coverage that had focused on images of tear gas and noisy demands for immediate justice.

A man who would give his name only as Randy said the demonstration was not about picking sides but about showing support for officers doing a difficult job.

"There are enough law enforcement groups investigating and that will take time," he said as passing cars honked their horns. "The police have a job to do and many people do not understand how hard it is." All were concerned about the risk to Wilson's family after his house was pictured on a local TV station, KSDK.

Many were police officers – or married to officers – and some discussed whether it would be appropriate to chant, "Hands up, Don't loot," a play on the Ferguson demonstrations where "Hands up, Don't shoot" has become a defining slogan.

"We're here to show that it's OK to support officer Wilson," said another, passing around a giant card that will be delivered to the policeman.

A two-person counter demonstration appeared across the street, with a sign reading: "Killer cops: Don't shoot." Ryan Wordsmith, a bartender, said police had been keen to smear Brown but so far had said nothing about the actual shooting.